Rear-strike typewriter mechanism



Dec- 29, 1953 H. JOHNSON 2,664,184v" REAR-STRIKE TYPEWRITER MECHANISMATTORNEY6- Filed NOV. 21, 1951 Patented Dec. 29, 1953 2,664,184REAR-STRIKE TYPEWRITER MECHAISM Harry Johnson, Elizabeth, N. J.,assignor to Ralph C. Coxhead CorporatiomNewark, N. J.,

a corporation of Delaware Application November Z1, 1951, Serial N0.257,587

18 Claims. l

This invention relates to typewriters and, more particularly, to atypewriter for typing on certain materials that cannot be satisfactorilytyped on with a conventional typewriter.

Certain nonabsorbentsubstances, including plastics, cannot be typed onwith the ordinary typewriter because of the need for penetration of theink, at least to some extent, into the surface. It has been foundthatplastics can be typed on by heating the type and using a thermoplasticor thermosensitive type ribbon. Such a typewriter is shown in ReschPatent 2,515,381, and the typewriter of the present invention is incertain respects an improvement over the type-v writer there shown. Thistypewriter is particularly useful for typing code `designations onlengths of flexible plastic tubing which may subsequently be severedinto short lengths for slipping over the ends of electrical wiring todesignate the identity of the wire.

The improvements of the present invention are incorporated in arear-strike typewriter of the sort known in the trade as the Vari-typerin which type is embossed upon a type shuttle slidably mounted on acylindrical anvil positioned in front of the article to be typed on, theshuttle being movable along theanvil responsive to operation of the typekeys to index any desired character at the printing point, a hammerbehind the anvil striking the object and driving it againstV the typeshuttle and a type ribbon interposed between the object and the shuttleto form thetype impression.

in the form shown of thepresent invention, an improved heating unit ismountedv on top of the anvil and heats the anvil whichin turn heats theshuttle. The typefribbon is thermosensitive type ribbon in which thepigment-issoitened by heat to form the printed impression. Instead ofthe usual spring-driven hammer. the hammer actionfis a combination of aninitial hammer low plus a steady hammer pressure so as to form a cleartype impression.

The typewriter Vof the present invention is particularly suited fortyping on plastic tubing and to that end incorporates an improved guidefor accommodating plastic tubing of various sizes.

Among the objects ofthe present invention are to provide a typewriterthat will type more clearly and uniformly on smooth,V nonabsorbentsubstances, including plastics; to provide such a typewriter in whichthe'type impression is uniform and produced by the combination of aninitial blow'plus a steady lpressure; to provide suchtypewriter.ofvsimple,V `depeifidable ilonstruction; to provide animproved typewrterfor typing on smallediameter, flexible tubing;A fandto generally improve typewriters of the class described.

Other cbjects fand' objects relatingftoudetails and economies ofconstruction will be' more readily apparent `from the detaileddescription to follow. 1

- My invention is clearly defined in the appended claims. In the claims,aswell as inthe description, parts are at times identified by specificnames for clarity and 'conveniencabutlsuchvno'- menclature is to bevunderstood as having'r the broadestfmeaning consistent with the .contextand with the concept of my linvention as distinguished from thepertinent, .prior art. The-best form in ywhich I have contemplatedapplyingimy invention is illustrated in the accompanying drawingsforming rpart of'this specification; in which:

Fig. 1 is a somewhat' diagrammaticfragmentary top plan viewfo'f atypewriter according-to the present invention, the forward portioniofthe typewritery including `the forward portionsfof the key levers'andassociated mechanism,fbeing omitted.

Fig. 2 is a somewhat diagrammatic "vertical section of the typewritertaken generally Yon the line y2-.-`2` ofr Fig, 1,'-portionsy of themechanism being omitted for clarity and convenience of i1- lustration.

Fig. 3 is an enlarged'vertical section of the anvil, shuttle, andheating unit takenthrough the vprinting point and showing therelationship of these parts with the tube guide and hammer.

Fig. 4 is a somewhat diagrammatic lillustration of a section of ilexibleVinylite tubing offthe sort which the present machine 'is adaptedztotype on.

Fig. 5 is a schematic wiring diagram of the electrical system employedin the typewriter.

kThe present invention will be describedasf'applied to a typewriter ofthetvpe known inthe trade as the Vari-typen although the'invention incertain of its broader aspects is capable with some modification ofbeing appliedequally well to other kinds of typewriters.

The typewriter shown and described'has been signed particularly forpermanent typing -upon 'e, smallfniameter, .Vinylite tubing ofthecommonly used: as terminal inselationfior u ring. it is desirable tohave the terminaltnsulation of complicated electrical wiring so'mark'edthat the individual wires may be identified readily at anylaterdate.lAccordingly, by qty-ping' approprate characters on Vinylite tubing andsubsequently cutting the tubing into short lengths positionable atterminal endings of wiring, a permanent, positive means of identifyingthe wiring is provided. Such a specimen of tubing is shown in Fig. 4 ofthe drawings. Of course, a typewriter embodying features of the presentinvention is capable of a multiplicity of other uses as well as typingon such tubing.

The typewriter shown in part in Fig. 1 is in general organizationsimilar to the commercial Vari-typer typewriter and is generally similarto the typewriter described in Trego Patent 1,967,278. This typewriterhas a carriage III which is mounted on a guide I3 for movement past aprinting point II. The carriage I is generally similar to the carriageof Resch Patent 2,515,381 and is provided with a clamp I 2 at each endof the carriage for receiving a length of tubing I4 to be typed on.

Movement of the carriage I0 past the printing point is controlled by anescapement mechanism I8. The carriage escapement mechanism may begenerally similar to that shown in Trego Patent 1,965,677 and provides auniform carriage escapement movement for all characters of the alphabet.A cylindrical anvil I5 is mounted just in front of the printing pointII. An arcuate type shuttle I6 conforming to the curvature of the anvilis slidably mounted for circumferential movement about the anvil toindex any desired type character at the printing point II. Preferably,the type shuttle, which is of the usual kind used in the Vari-typer, hasthree lines of embossed type characters thereon, the anvil and shuttlebeing raised by operation of the Cap and Fig. shift keys, but the anvilbeing otherwise fixed.

A hammer I'I is mounted on a horizontal pivot I9 under the carriage andextends in a generally semicircular form to the rear of the carriage,terminating in a head or impression-forming portion 20 located behindthe tubing I4 at the printing point. The hammer is spring operated inits printing stroke, being driven forward against the tubing by a hammerspring 23 to form each printed impression. A helical spring 21 carriedon a hammer check rod 29 depending from the lower rear portion of thehammer I'I checks forward movement of the hammer and provides a hammerStroke of the desired charac teristics for ordinary typing. The hammerI'I is returned by an escapement mechanism powered by a spring motor 2|mounted on the back of the typewriter and intermittently rewound by anintermittently operated electric motor 22. The escapement mechanism I8controls operation of the hammer Il as well as spacing movement of thecarriage I0 as shown in Trego Patent 1,965,- 677 in order to properlycorrelate hammer movement and carriage spacing.

Operation of the hammer I1 is initiated by raising the forward portionof the trip frame 24 (Fig. 2). The trip frame 24 comprises a bail whichextends above the rear end of each of the printing keys. The trip frameis operated upon actuation of any of the printing keys and also uponactuation of the space bar, in order to operate the carriage escapementmechanism I8 and cause spacing movement of the carriage. Accordingly,upon actuation of the space bar, the rear end of the space bar lever 25,which is generally similar to the rear ends of the printing key levers,raises the trip frame 24 also in producing carriage spacing, thusinitiating actuation of the hammer. However, upon operation of the spacebar, a space bar hook (not shown) is interposed in the path of thehammer II to check or arrest forward or counterclockwise movement of thehammer short of a complete impressionforming stroke but still allowingsuflcient movement of the hammer to actuate the escapement mechanism I8and produce carriage spacing. This general organization for checking thehammer short of a full stroke upon operation of the space bar is knownand does not constitute part of the present invention.

A type ribbon 30 is interposed between the tubing I4 and the typeshuttle I6 at the printing point, this type ribbon being fed from leftto right in the customary manner as indicated in Fig. 1. The type ribbon30 is a single-use, thermosensitive type ribbon, known in the trade asbranding tape, which is capable of forming type impressions when theribbon or the type is heated to an elevated temperature so as soften theribbon pigment for the printing operation. This ribbon is fed from arelatively large reel 3I mounted on the left side of the typewriter andis progressed by feed rolls 32 at the right side of the typewriter (seeFig. 1), the ribbon being discarded after one use.

According to the present invention, the anvil I5 is heated to anelevated temperature by a heating unit mounted on top of the anvil andcomprising a circular, metallic cap 34 of the approximate diameter ofthe anvil and having a depending skirt in thermal contact with the topedge of the anvil throughout its circumference. The cap 34 is heated toelevated temperature by an electrical resistance heating element 36contained within the cap, the heat of the cap being transmitted to theanvil and in turn to the shuttle I6. The shuttle is maintained at a moreor less constant temperature of about 200 F., the organization beingsuch that, after the shuttle has been raised to operating temperature,the heat losses from the anvil, shuttle, and cap are approximately equalto the heat input; and, therefore, a thermostat or other heat control toprevent overheating of the anvil and shuttle is not required.

In printing with a thermosensitive ribbon such as the ribbon 30, it isdesirable to have an initial impact between the type and the work,together with a steady pressure for an appreciable period of time tosoften the ribbon pigment and form the impression. Accordingly, in atypewriter of the present invention, a solenoid-operated mechanism isprovided to increase and maintain for a period the hammer pressureagainst the work when forming the printed impression. This mechanismcomprises an electrical solenoid 31 mounted on the typewriter frame, thesolenoid drawing an iron core 38 downwardly to operate a bell cranklever 39. which is mounted for rotation about a fixed pivot 4I), one endof the bell crank lever being connected with the core 38 by a link 4I. Aroller 42 is mounted on the other end of the bell crank lever 39 and,upon actuation of the solenoid 31, engages against and presses forwardlyupon the rear edge of the hammer I I so as to press forwardly on thehammer and provide a steady and continuous forward pressure of thehammer against the tubing I4 so long as the solenoid is actuated.

The electric circuit of the typewriter is indicated in the wiringdiagram of Fig. 5. The motor 22 is energized to wind the spring motor 2Iwhenever the spring motor becomes unwound, a switch 43 being closed byunwinding of the motor 2I tot` cause:v operation of the.J motor and;lbeing opened upon. the. spring.` motor again' being Wound. A nlter`48...may be. insertedgin the line iff -desired inA order to prevent.electricahinterference: if` the typewriter= is. to be operatedl onshipboard. VThis portionof: the` wiring isf gen-- erally old and? has'beenused in the;.Vari-typer forv a;y number of' years.

The circuit totthe1 heating unit, including-.the heating element 36andfth'efsolenoid' 3:11, isfcontrolled by a manually operatedelectric-switcnM which may be: a toggle switch: mounted" on-r theforward portionofithetypewriter frame. Closing of' thisA switchenergizesthe heating uniteSBfand the circuitlto the solenoid3'lf,whichzisponnected in parallel with the heatingv unit SBandf con trollediby three switches connected-in series; all of1 whichrnay: be of theVmicroswitch: type. The first of these switches is a hammer-operatedswitchy 45, which isnOrmally. open butfwhich is moved to closed positionby a projectionI 46 mounted on the lower end ofthe hammerl check rod 29,this switch being closed? as the. hammer approaches forwardorimpression-forming position and being reopened asfthe hammer movesrearwardly from extremeforward position. This switch causes the solenoid31 to be energized* so as to furnish the proper hammer pressure forforming the printed impression, as: above4` described.

A` second' ortrip-frame-operat'ed switch 41,' in series-with thehammer-operated switch 45y and also normally-open, is operated by link48'to close the switch upon the trip framebeingraised' by operation ofany printing key or the-space bar 2.5! and remains closed until theprinting key or space bar is released, so as to'permit tliehammer il'tofreturn tonormal position. Closingof the trip Yframe switch 41 occursv before releaseoff' the hammer II- for'- its printing stroke andbeforeclosing of'the hammer-operated switch 45;- and", therefore, the solenoid3f'l'is1energized1upon clos'- ing of the hammer-operated switch.However, the hammer-operated switch 45 remains-closed until the hammercommences'its return to rear* ward or normal position, which cannotoccur unftilthe solenoid is no longer energized; TheY circuit throughthe solenoid 3l' is interrupted by opening of the trip-frame-operated;`switch 41,` which occurs-when the printing key is released; and the tripframe drops to normal position. Ac'- cordingly, theY solenoid 3lisenergizedby'closing ofthe hammer-'operated switch 45', and thejci'rcuitthrough the solenoid' is interruptedI upon opening ofthetrip-irame-operated`-switch 4T;

A space-bareoperated switch 49, which YisA normallyclosed, is also inseries with the switchesA [t5 and't'l. This switch which is operated bya` link 53 connected to the space barlever 25v is` opened upon operationofthe spacef'barto raise the trip frame 24 and remains open until thebar is released andthe space barA lever 25 returns to normal position.Accordingly, upon operation ofv the space bar, the space-bar-operatedswitch lli!`- is openv while the trip-'frameoperated switch 41 is closedand vice versa, and thereby energization of the solenoidv 31A isprevented as thev hannrierv l'l'move forward'finiits curtailed strokeduring 'operation of the space-barin: order to operate theescapementmechanismfor carriage,spacing.v

summarizing theoperation offtheporti'on off the electrical system'particularly concernedwitli.. the typing with a heat-sensitive ribbon;theihealr-- ingunit ,36 iscontinuouslyl energizediso as .toiheattheeanvll; l'lf-.and'typeg-shuttle |16: ton the desiredmento'-retum:tozrearwarclnormal position. Upon operation off' the space.bar; the spaceebar-oper ated'. switch.. dBi-ls' opened` so` as toprevent ener-- g-izatiorn of: theisolenold, even1though both of theeswitches: 45;.and. 4"y are closed;

`Arpair oflguides andi'l aremount'ed onthe typewriter frame.l at Itheleftxand right-hand sides, nespectively,. of fthe5 printing point'- forsupportinglthe tubing; M2. against" sagging. These guides have anupwardly opening, generally-U- shaped; contoun'as indicated? in@ Fig. 3for lreceiving, andaV supportingethe tubing. vThe interiorcontourfofieachfof 'the guidesis generally circular except: for.arconyerging forwardly extending guide portion; ordnotclr.v 525i forvertically aligning th'e1tubingwithathe topmost linefoffI embossed typeon theishuttle,y this lineiofftype` being operative when the shiftfkeysare not operated. rlC-he guides 59? and'v Si providefonallgning'tubing'of various diameters:with-.ther'shuttle IIS-sofasv to form cleartypeilmpressions on the..tubing;

1. vIn.. a rear'-st'rilrev typewriter, embossed type,a..pivotallyvmountedi'hammer, a rhammer spring biasingthe hammer.`forwardly for' a printing stroke to drive work to be typedione-againstthe type', an?escapementtmeclianism for' controlling operation of thehammer, v andv mechanism, including; an* electrioalsolnoid energizedupon fonwardimovementf ofthe-harnmerinits printing stroke-"forrnaintainingran-L increased pressure of the hammen against:work to betyped' on during formationf of? a. type impression.

2. In. a: rearestrikef typewriter for printing with the-faioly offheat-;- aw heated typev shuttle havin?,r

type'y symbols l embossed thereon andl movable to; in'dexf-selected?vsymbolsj at" a printingr point, movable;t carriage for supporting workto be typed on; aitliermosensitive type' ribbon interposed between thework-and the shuttle, a ham- 1 mer inrear-fthe-sliuttle fordriving thework againstjitheftyperribbomandshuttle to form al typesimpression;l ar`spring for'driving the hammer"forwardl'yfv against tlflework-AA inprinting stroke,A andmechanism,A including an electrical' sclenoidroperated`r as;v thet hamm-er approaches the; worktforinereasin'gw andmaintaining pres'- sure .off the..hammer againsty the` work duringfermation` ofi the;y type impression;

Ina rear-str-ikeftype riterhaving'a movable carriageifonholding worktofbe typed on, printingi: keys, embossedfltype indexed at the printingpointl inf; response l.tooperation of the printing leeys; a.typefribbon'g'a. pivotally mounted hammer for driving:U theyworkragainstv` the typef and ribbon, means biasing the hammerforwardly-foraiprinting'strokeyan. escapenrient` mechanism forcnntrogllingt onerationzon'theihammer: andi a tripv frames m'ovedi-rominormali position; by' operation ovanyy-.ofesaidi printingg;A keysi to:operate theA i escapementf.l mechanism; ,relectricali means open atedupon forward movement of the hammer for maintaining increased pressureof the hammer against the work during formation of the type impression,and means operated by return of the trip frame to normal position forinterrupting the circuit to said electrical means upon release of aprinting key whereby rearward oscillation of the hammer is permitted.

4. In a rear-strike typewriter having a movable carriage for holdingwork to be typed on, printing keys, embossed type indexed at theprinting point in response to operation of the printing keys, a typeribbon and a pivotally mounted hammer for driving the Work against thetype and ribbon; means for driving the hammer forwardly against the workfor a printing stroke, electrical means operated upon forward movementof the hammer for pressing forwardly on the hammer during formation ofthe type impression, and means operatively connected with the printingkeys for interrupting the circuit to said electrical means upon releaseof a printing key, whereby rearward oscillation of the hammer ispermitted.

5. In a rear-strike typewriter for printing with the aid of heat, a typeshuttle having type symbols embossed thereon and movable to indexselected symbols at a printing point, a movable carriage for supportingwork to be typed on, a thermosensitive type ribbon interposed betweenthe work and the shuttle, a hammer in rear of the shuttle for drivingthe work against the type ribbon and shuttle to form a printedimpression, a spring for driving the hammer forwardly against the workin its printing stroke, and mechanism, including an electrical solenoidoperated as the hammer approaches the work, for increasing andmaintaining pressure of the hammer against the Work during formation ofa type impression.

6. In a rear-strike typewriter for printing with the aid of heat, typeindexed at a printing point, a movable carriage for supporting work tobe typed on, a thermosensitive type ribbon interposed between the workand the shuttle, a hammer in rear of the shuttle for driving the workagainst the type ribbon and shuttle to form a printed impression, aspring for driving the harnmer forwardly against the work in itsprinting stroke, and mechanism, including an electrical solenoidoperated as the hammer approaches the Work, for increasing andmaintaining pressure of the hammer against the work during formation ofthe printed impression.

7. In a typewriter for printing with the aid of heat and having athermosensitive type ribbon, an anvil having a cylindrical outersurface, an arcuate type shuttle having type characters embossed thereonand having an arcuate rear surface mounted for sliding movement alongthe outer surface of the anvil to index selected type at a printingpoint, and a cylindrical heating unit mounted above the anvil andcomprising a cylindrical, metallic cap having a generally flat, circularportion and having a depending, cylindrical skirt in thermal contactwith the anvil throughout its circumference, and an electricalresistance heating coil mounted on the underside of the circular portionfor heating the anvil and shuttle.

8. In a typewriter for printing with the aid of heat and having athermosensitive type ribbon, an anvil having a cylindrical outersurface, an arcuate type shuttle having type characters' embossedthereon and having an arcuate rear surface mounted for sliding movementalong the outer surface of the anvil to index selected type at aprinting point, and a cylindrical heating unit mounted above the anviland comprising a cylindrical, metallic cap having a generally flat,circular portion and having a depending, cylindrical skirt in thermalcontact with the anvil throughout its circumference, and an electricalheating means mounted within the cap for heating the anvil and shuttle.

9. In a rear-strike typewriter having embossed type indexed at aprinting point and a type ribbon, a hammer for driving Work to be typedon against the type and ribbon and comprising an elongated hammer armmounted for oscillation on a fixed pivot and a work-engaging head, andhammer-operating means, including a bell crank mounted on a fixed pivot;a roller mounted on the free end of one arm of the bell crank andadapted to engage against the rear of the hammer arm between the hammer'arm pivot and the head, and electromagnetic means, including a solenoidand a core linked with the other arm of the bell crank, for oscillatingthe bell crank about the pivot to press the hammer against the workduring formation of a type impression.

10. In a rear-strike typewriter having embossed type indexed at aprinting' point and a type ribbon, a hammer for driving work to be typedon against the type and ribbon and comprising an elongated hammer armmounted for oscillation on a xed pivot and a work-engaging head; andhammer-operating means, including a bell crank mounted on a fixed pivot,one arm of the bell crank being adapted for engagement against the rearof the hammer arm between the pivot and the head, and electromagneticmeans connected with the other arm of the bell crank for oscillating thebell crank about the pivot to press the hammer against the work duringformation of a type impression.

11. In a rear-strike typewriter, type indexed at a printing point, apivotally mounted hammer for driving work to be typed on against thetype, a hammer spring biasing the hammer forwardly for a printingstroke, an escapement mechanism for controlling operation of the hammer,and electrically operated mechanism including an electrical solenoidenergized upon forward movement of the hammer in its printing stroke formaintaining an increased pressure of the hammer against work to be typedon during formation of a type impression.

12. In a rear-strike typewriter, type indexed at a printing point, apivotally mounted hammer for driving work to be typed on against thetype, a hammer spring biasing the hammer forwardly for a printingstroke, an escapement mechanism for controlling operation of the hammer,and mechanism including an electrical solenoid energized upon forwardmovement of the hammer in its printing stroke for maintaining anincreased pressure of the hammer against work to be typed on duringformation of a type impression.

13. In a rear-strike typewriter having a movable carriage for holdingwork to be typed on, printing keys, embossed type indexed at a printingpoint in response to operation of the printing key, a space bar, a typeribbon, a hammer for driving the work against the type and ribbon, meansbiasing the hammer forwardly for a printing stroke, an escapementmechanism for controlling operation of the hammer and spacing movementof the carriage, and a trip frame moved from normal position to operatethe escapement mechanism by operation of any of the printing keys or thespace bar; electrical means for maintaining increased pressure of thehammer against the work during formation of the type impression, anelectrical switch actuated by forward movement of the hammer foroperating said electrical means, a second electrical switch operated byreturn of the trip frame to normal position for interrupting the circuitto said electrical means upon release of the printing key wherebyrearward oscillation of the hammer is permitted, and a third electricalswitch operated by actuation of the space bar for preventing operationof said electrical means upon actuation of the space bar.

14. In a rear-strike typewriter having a mov able carriage for holdingwork to be typed on, printing keys, embossed type indexed at a printingpoint in response to operation of the printing I key, a space bar, atype ribbon, a pivotally mounted hammer for driving the Work against thetype and ribbon, means biasing the hammer forwardly for a printingstroke, an escapement mechanism for controlling operation of the hammerand spacing movement of the carriage, and a trip frame moved from normalposition to operate the escapement mechanism by operation of any of theprinting keys or the space bar; electrical means operated upon forwardmovement of the hammer for maintaining increased pressure of the hammeragainst the work during formation of the type impression, means operatedby return of the trip frame to normal position for interrupting thecircuit to said electrical means upon release of the printing keywhereby rearward oscillation of the hammer is permitted, and meansoperated by actuation of the space bar for preventing operation of saidelectrical means upon actuation of the space bar.

15. In a rear-strike typewriter having a movable carriage for holdingwork to be typed on, printing keys, embossed type indexed at a printingpoint in response to operation of the printing keys, a space bar, a typeribbon, a pivotally mounted hammer for driving the work against the typeand ribbon, means biasing the hammer forwardly for a printing stroke, anescapement mechanism for controlling operation of the hammer and spacingmovement of the carriage, and a trip frame moved from normal position tooperate the escapement mechanism by operation of any of the printingkeys 'or the space bar; electrical means for maintaining increasedpressure of the hammer against the work during formation of the typeimpression, and three electrical switches connected in series with saidelectrical means, one of said switches being normally open and closed byforward movement of the hammer, a second of said switches being normallyopen and closed by movement of thetrip frame from normal position, and athird of said switches being normally closed and opened byactuation ofthe space bar. y

y16. In a rear-strike typewriter having a movable carriage for holdingwork to be typed on, printing keys, embossed type indexed at theprinting' point in response to operation of the printing keys, a typeribbon and a pivotally mounted hammer for driving the work against thetype and ribbon; means for driving the hammer forwardly against the workfor a printing stroke, electrical means for pressing forwardly on thehammer during formation of the type impression, an electrical switch incircuit with the electrical means and actuated by forward movement o fthe hammer for yoperating said electrical means, and an electricalswitch operatively connected withy the printing keys for interruptingthe circuit to said electrical means upon release of a printing key topermit rearward oscillation of the hammer.

17. In a rear-strike typewriter having movable type indexed at theprinting point and a hammer for driving Work to be typed on against thetype to form a type impression, a guide for supporting flexible tubingof various sizes at the printing point, said guide comprising a.substantially at plate having a generally U-shaped inner contour forreceiving the tubing and the forward portion of the inner wall of theguide being notched to form a converging guide portion directed towardsthe type.

18. In a typewriter for printing with the aid of heat and having athermosensitive type ribbon, an anvil having a cylindrical outersurface, an arcuate type shuttle having type characters ernbossedthereon and having an arcuate rear surface mounted for sliding movementvalong the outer surface of the anvil to index selected type at aprinting point, and a heating unit mounted above the anvil andcomprising a metallic cap covering the anvil and having a dependingcircular skirt in thermal contact with the anvil throughout itscircumference, and an electrical resistance heating unit mountedadjacent the underside of the metallic cap for heating the cap, anvil,and shuttle.

HARRY JOHNSON.

References Cited in the file o1' this patent UNITED STATES PATENTS nNumber Name Date 718,758 Harrison Jan. 20, 1903 2,007,228 Trego July 9,1935 2,007,229 Trego July 9, 1935 2,308,461 Talley f Jan. 12, 1943

